Control of Grape Powdery Mildew, 2009 Field Trials
University of California, Davis, CA
Christopher N. Janousek, Ian S. Bay, and W. Douglas Gubler
Department of Plant Pathology
Objective: Powdery mildew is caused by the pathogen Uncinula necator, which is common in Vitis species and thrives in warm, humid environments. The Pathogen can be treated with a range of anti-mildew compounds, however, after several years of use a resistance development has been documented in the field, suggesting that new materials or novel cultural practices may need to be eventually integrated into current control regimes.
Method: Five adjacent trials were conducted at Herzog Ranch, located near Courtland, CA. Spraying commenced in April and commenced in July after a 12 week period. Trial I consisted of IR-4 funded biofungicide research focusing on capriylic acid and Actinovate. Trials II-V included varying fungicide products. The frequency of spraying varied from weekly application to 21 day intervals. Treatment consisted of an unsprayed control, three concentrations of Flint (trifloxystrobin), one applied alone, one with Companion® (Bacillus subtilis), and one with Actionvate® (Streptomyces lydicus), one concentration of AMV (caprylic acid), one concentration of Actinovate with Serenade® MAX (Bacillus subtilis), and one concentration of Serenade MAX.
Results: Following 12 weeks of fungicide application, Biological fungicides reduced the disease severity in general, however, they were more effective when used in a combination program. In the unsprayed control, disease incidence was 100% and severity exceeded 90%. Flint was greatly effective when applied alone reducing the both the incidence and severity. When Flint was paired with Companion, it outperformed the field reducing disease incidence by over 20% and disease severity by over 80% from the unsprayed control. (Figures 1 & 2).
Figure 1 - Incidence
Figure 2 - Severity